The invention relates to an organic light-emitting diode for luminous displays, luminaires, solid-state image intensifiers, color monitors, color display screens and the like, which diode comprises a laminated composite comprising, in succession, a substrate layer, a first electrode layer, a layer including a p-conductive organic material, a layer including a complex compound of terbium with organic ligands, a layer including an n-conductive material and a second electrode.
Light-emitting diodes (LED) in accordance with the state of the art generally are semiconductor diodes, that is diodes which are constructed by means of inorganic semiconductors, such as doped zinc sulphide, silicon, germanium, or III-V semiconductors, such as InP, GaAs, GaAlAs, GaP or GaN containing appropriate dopings. Since a number of years, efforts are being made to develop luminescent radiation sources whose emitter material is not an inorganic semiconductor yet an organic, electroconductive material.
Light-emitting diodes comprising luminous layers of organic materials are clearly superior, in some respects, to light sources of inorganic materials. One advantage is that they can be readily moulded and exhibit a high elasticity, thus enabling new applications for luminous displays and display screens. These layers can be readily manufactured as large-surface, flat and very thin layers for which, in addition, only a small amount of material is necessary. Said layers are characterized by a remarkably high brightness in combination with a small drive voltage.
Besides, the color of the emitted light can be varied in wide ranges from approximately 400 nm to approximately 650 nm by the choice of the luminescent substance. These colors demonstrate a remarkable luminance.
Also combinations of electroconductive organic materials and metallo-organic compounds of the rare earth metals have been used for organic, light-emitting diodes in order to obtain color displays having an improved color purity and exact color points in accordance with the EBU standard. In DE 44 28 450, a description is given of an organic electroluminescent component comprising a multilayer structure including a substrate layer, a first transparent electrode layer, one or more optoelectronically functional layers comprising, optionally, one or more p-conductive organic materials with one or more singlet states and one or more triplet states and comprising a luminescent material including one or more complexes of a rare earth metal ion with organic ligands, said rare earth metal ion having are emitting state and the organic ligands having one or more singlet states and one or more triplet states, and said optoelectronically functional layer(s) further optionally comprising one or more n-conductive, organic materials with one or more singlet states and one or more triplet states and a second electrode, the lowest-energy triplet state of the ligands being lower than the lowest-energy triplet states of the n-conductive and/or p-conductive organic material, and being higher than the emissive state of the rare earth metal ion. The rare earth metal ion may be, for example, a terbium (III) ion.
In these organic light-emitting diodes the layers of p-conductive or n-conductive material and the layer having a complex compound of terbium can be manufactured in a different way. The complex compound of terbium can be dissolved, for example, alone or together with the p-conductive material and the n-conductive material in a matrix of a polymer, for example polycarbonate, polymethacrylate. The complex compound of terbium may alternatively be vapor-deposited, alone or together with the p-conductive and the n-conductive material, in the form of a layer.
In order to be suitable for these manufacturing methods, the complex compound of terbium should be soluble in the non-polar solvents, which dissolve the polymers, and it should be soluble in the polymers themselves. In addition, it should be possible to evaporate and sublimate the complex compound of terbium in an undecomposed state.
Therefore, it is an object of the invention to provide an organic light-emitting diode comprising a complex compound of terbium with organic ligands, which diode can be readily manufactured.
In accordance with the invention, this object is achieved by an organic light-emitting diode comprising a laminated structure including, in succession, a substrate layer, a first electrode layer, a layer with a p-conductive organic material, a layer including a complex compound of terbium with organic ligands, a layer with an n-conductive material and a second electrode, the complex compound of terbium with organic ligands having the following composition: TbL(C2H5OH)2, wherein L=N,Nxe2x80x2,Nxe2x80x3-Tris-(3-R1xe2x80x94,5-R2-2-X-benzyl-1,4,7-triazacyclononane, wherein X =xe2x80x94Oxe2x80x94, COOxe2x80x94, R1=CH3, C2H5, C3H7, i-C3H7, t-C4H9, OCH3, OC2H5, OC3H7, -O(t-C4H9, F, Cl, Br, NO2 and R2=CH3, C2H5, C3H7, i-C3H7, t-C4H9, OCH3, OC2H5, OC3H7, -O(t-C4H9)-F, Cl, Br, NO2.
This neutral terbium complex comprising the macrocyclic chelate ligand L having 1,4,7-triazanonane as the parent substance enables a surprisingly high emission quantum efficiency in the diode to be attained. In addition, the complexes are mononuclear, so that they are readily sublimable in the undecomposed state. In the undecomposed state, they are soluble in non-polar solvents, for example hydrocarbons such as toluol, cyclohexane, halogenated hydrocarbons such as dichloroethane, dichloromethane, chloroform or chlorobenzene, and in polymers such as polyacrylate, polystyrole and the like.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.